Electrical device allowing for increased device densities

ABSTRACT

A device comprising a circuit, a lead having a first end connected to the circuit and having a second end, and a deformable structure connected to the second end of the lead. The invention may be embodied on a circuit board, so that the circuit board includes a substrate and a deformable structure connected to said substrate.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of co-pending U.S. patentapplication Ser. No. 09/205,796, filed Dec. 4, 1998.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention is directed to a device that can be madesmaller and with improved electrical characteristics than prior artdevices and, more particularly, to a semiconductor device that can bemade with a package that allows for greater device densities on circuitboards, shorter lead lengths, more tolerance to non-uniformities, andimproved cooling.

[0004] 2. Description of the Background

[0005] Electronic products typically contain a large number ofelectrical devices organized on one or more substrates, also known ascircuit boards. The efficient packaging of those devices is an importantfactor in the product's performance. One way to improve performance isto increase the density of electrical devices on the substrate. Forexample, density may be increased by decreasing the size of the devices,thereby increasing the number of devices that can be placed on a givensubstrate.

[0006] One way to increase device density is to use vertical packaging,which places devices perpendicular to the substrate. Vertical packagingallows for many more devices to be placed on a substrate becausevertically oriented devices have smaller footprints than horizontallyoriented devices. However, vertical packaging is subject to packageinstability (i.e. tipping over), particularly during processing stepsinvolving poor adhesion between the device and the substrate, such assolder reflow. That instability is caused, in part, by non-uniformitiesin both the substrate and device. As a result, vertical packagingrequires additional steps to create more uniform devices and substrates,and to stabilize the devices during some processing steps.

[0007] Conventional devices and substrates also suffer from otherproblems caused by non-uniformities. For example, bending of deviceleads and poor contact between the device and substrate may result ifthe device and substrate are not uniform. Such problems require thatdevice leads be lengthened to allow for greater flexibility tocompensate for the non-uniformities. Longer leads, however, may resultin the lead bending and possibly creating a short between conductors onthe substrate. In addition, longer leads may cause detrimentalelectrical characteristics, such as increased resistance, increasedcapacitance, and decreased speed. Furthermore, longer leads tend toincrease instability problems when there is poor adhesion between thedevice and the substrate.

[0008] Thus, a need exists for an improved device to allow for increaseddevice densities without the deficiencies of the prior art.

BRIEF SUMMARY OF THE INVENTION

[0009] The present invention is directed to a device comprising acircuit, a lead having a first end connected to the circuit and having asecond end, and a deformable structure connected to the second end ofthe lead. The invention may be embodied on a circuit board, so that thecircuit board includes a substrate and a deformable structure connectedto said substrate.

[0010] The present invention solves the shortcomings of the prior art byproviding for higher device densities, shorter lead lengths, and moretolerance of non-uniformities, such as those in devices and substrates.Those and other advantages and benefits of the present invention willbecome apparent from the description of the invention provided

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0011] For the present invention to be clearly understood and readilypracticed, the present invention will be described in conjunction withthe following figures wherein:

[0012]FIG. 1 is a perspective view of a circuit board including asubstrate, a device, and a deformable structure between the circuit andconductive paths on the substrate;

[0013]FIG. 2 is a cross-sectional view along line II-II of the circuitboard illustrated in FIG. 1;

[0014]FIG. 3 is a perspective view of a circuit board includingdeformable structures in elongated form on the substrate;

[0015]FIG. 4 is a cross-sectional view of a device including adeformable structure attached to leads of the device;

[0016]FIG. 5 is a perspective view of a device including an integratedcircuit partially enclosed in a package;

[0017]FIG. 6 is a cross-sectional view along line VI-VI of the deviceillustrated in FIG. 5;

[0018]FIG. 7 is a perspective view of a device including leads formedfrom tab tape;

[0019]FIG. 8 is a cross-sectional view along line VIII-VIII of thedevice illustrated in FIG. 7; and

[0020]FIG. 9 is a cross-sectional view of a device including leadsformed from multiple layered tab-tape.

DETAILED DESCRIPTION OF THE INVENTION

[0021] It is to be understood that the description of the invention hasbeen simplified to illustrate aspects that are relevant for a clearunderstanding of the present invention, while eliminating, for thepurpose of clarity, other elements. Those of ordinary skill in the artwill recognize that other elements may be desired and/or required.

[0022]FIG. 1 is a perspective view of a circuit board 10 including asubstrate 12, such as a circuit board, having conductive paths 14 fortransmitting signals, a device 16 having leads 18 for transmittingsignals to and from the device 16, and a deformable structure 20connecting the substrate 12 to the device 16.

[0023] The device 16 may be an integrated circuit, a discrete component,or any other device that is connected to a substrate. In one embodimentof the present invention, the device 16 is a memory device. In thatembodiment, the device may be dynamic memory or static memory. The leads18 of the device 16 may be for surface mount connection to the substrate12.

[0024] The deformable structures 20 connect the substrate 12 to thedevice 16. In the present embodiment, the deformable structures 20connect the conductive paths 14 of the substrate 12 to the leads 18 ofthe device 16. The deformable structures 20 may be connected to thesubstrate 12 and the device 16 with conductive or non-conductiveadhesives. Alternatively, the deformable structures 20 may themselves beadhesive so that additional adhesive is not required.

[0025] The deformable structures 20 may be of a number of types andshapes. For example, the deformable structure may be of a structure forconnecting a single lead 18 to a single conductive path 14, asillustrated in FIG. 1. In that embodiment, the deformable structures 20may be located at discrete locations on the substrate 12, such as atplaces where leads 18 connect to conductive paths 14. Alternatively, asingle deformable structures 20 may connect several leads 18 to severalconductive paths 14, as described in more detail hereinbelow withrespect to FIGS. 3 and 4. The deformable structures 20 may be placed ateach location on the substrate 12 where the leads 18 connect to theconductive paths 14. Alternatively, the deformable structures 20 may beselectively placed at locations where non-uniformities are likely toexist. Thus, there may be as few as one deformable structure 20, or asmany deformable structures 20 as there are leads 18.

[0026] The deformable structures 20 may be compressed between the leads18 and the substrate 12. That ability to be compressed compensates fornon-uniformities that may exist, such as in the substrate 12, theconductive paths 14, the device 16, and the leads 18. That compensationreduces or eliminates bending of the leads 18 and poor contact betweenthe leads 18 and the conductive paths 14 that would otherwise be causedby the non-uniformities. Furthermore, the deformable structures 20eliminate the need to lengthen the leads 18, thereby allowing forshorter leads 16, shorter signal paths, and increased performance.Shortening the leads 18 also reduces or eliminates the risk of surfacemount leads rubbing the bottom of the device 16 or rubbing the substrate12, thereby reducing the risk of short circuits.

[0027] The deformable structures 20 may be any of several differentmaterials. Fore example, the deformable structures 20 may be a polymer,such as silicone. The deformable structures 20 may also be resilient,such as when formed from elastomers, although the deformable structures20 do not necessarily have to be resilient. The deformable structure 20may be conductive or non-conductive, depending on the particularapplication.

[0028]FIG. 2 is a cross-sectional view along line 11-11 of the circuitboard illustrate in FIG. 1. A conductor 24 may be disposed over thedeformable structure 20 and in contact with the leads 18 and theconductive paths 14. The conductor 24 may be, for example, a conductiveadhesive or a conductive tape used to secure the leads 18 to thedeformable structures 20. The conductor 24 may be applied on individualdeformable structures to provide an electrical connection between onelead 18 and one conductive path 14. Alternatively, the conductor 24 maybe applied across several deformable structures 20 where an electricalconnection is desired between several leads and/or several conductivepaths 14.

[0029] The conductor 24 may be eliminated if connection between theleads 18 and the conductive paths 14 are not desired, such as if theleads 18 are only needed to support the device 16. The conductor 24 mayalso be eliminated if the deformable structures 20 are conductive. Inone embodiment, the deformable structures 20 are both conductive andadhesive, thereby eliminating the need for additional adhesives andconductors, but still providing electrical connection between the leads18 and the conductive paths 14.

[0030]FIG. 3 is a perspective view of a circuit board 10 includingdeformable structures 20 in elongated form on the substrate 12. Thedeformable structures 20 may extend over part or all of the substrate12. The deformable structures 20 may be non-conductive so that any oneof the deformable structures 20 may contact several conductive paths 14and several leads 18 but not cause a short circuit. In that embodiment,conductors 24 may be used to electrically connect individual leads 18 toindividual conductive paths 14, as discussed hereinabove.

[0031]FIG. 4 is a cross-sectional view of a device 16 includingdeformable structures 20 attached to the leads 18. In that embodiment,the deformable structures 20 may be attached to the leads 18 of thedevice 16 prior to connecting the device 16 to the substrate 12. Asdescribed hereinabove, the deformable structures 20 may be adhesives, oradhesives may be used to attach the deformable structures 20 to theleads 18.

[0032]FIG. 5 is a perspective view of a device 16 including anintegrated circuit 30 partially enclosed by a package 32, and leads 18extending from the package 32. The device 16 may be, for example, anapplication specific integrated circuit or a memory device. The device16 illustrated in FIG. 5, as well as the devices 16 described hereinbelow with respect to FIGS. 6-9, may be used with or without thedeformable structures 20. If the device 16 is used without thedeformable structures 20, it may be applied directly to flex tape orconductive traces on a substrate 12.

[0033]FIG. 6 is a cross-sectional view along line VI-VI of the device 16illustrated in FIG. 5. The integrated circuit 30 has an active area 38including electrically conductive connections to logic gates in theintegrated circuit 30. The integrated circuit 30 also includes anon-active area 40 which does not contain electrically conductiveconnections to logic gales forming the integrated circuit 30.

[0034] The package 32 encloses the active area 38 of the integratedcircuit 30, as is conventionally done, but does not enclose a portion ofthe non-active area 40. The non-enclosed portion of the non-active area40 is exposed to ambient environment. Exposing a portion of thenon-active area 40 of the integrated circuit 30 facilitates cooling ofthe integrated circuit 30. In addition, exposing a portion of theintegrated circuit 30 allows for a smaller profile of the device 16,because the package 32 is thinner, thereby allowing for increaseddensity of devices 16 on a circuit board.

[0035] The leads 18 may be connected to the active area 38 of theintegrated circuit 30 with lead bonds 44 in a lead-over-chip manner. Alead-over-chip design offers an advantage of making connections near thecenter of the integrated circuit 30, as opposed to near the edge of theintegrated circuit 30. As a result, the edge of the active area 38 ofthe integrated circuit 30 may be engaged by the package 32 to moresecurely hold the integrated circuit 30. Alternatively, the leads 18 mayalso be connected to the integrated circuit 30 using a design other thanlead-over-chip. Two such examples are tab bonding and peripheral bondpads that provide for sufficient space near the edge of the integratedcircuit 30 to allow for engagement by the package 32. Furthermore, theintegrated circuit 30 may be engaged by the package 32 at only thesides, without engaging the active area 38.

[0036]FIG. 7 is a perspective view of a device 16 including leads 18formed from a flexible conductor adhesive, such as tab-tape. A portionof the leads 18 may be attached to the package 32 with the adhesive. Forexample, the leads 18 may be attached to the outside of the package 32from a point where the leads 18 exit the package to a point where theleads 18 are to be attached to another structure, such as a substrate.The leads 18 in that embodiment may be used with the deformablestructures 20 described hereinabove, and may also be used with exposedintegrated circuit 30 described hereinabove.

[0037]FIG. 8 is a cross-sectional view along line VIII-VIII of thedevice 16 illustrated in FIG. 6. A spacer 50 may be used so that theleads 18 are away from the package 32, thereby reducing the risk of thepackage 32 contacting the substrate 12. The spacer 50 may be made of thesame materials as the deformable structure 20 described hereinabove withrespect to FIGS. 1-4, so that the spacer 50 compensates fornon-uniformities, such as on the substrate 12. The spacer 50 may also bea dielectric so as to insulate signals on the leads 18.

[0038]FIG. 9 is a cross-sectional view of a device 16 having leads 18formed from multiple layers of tab-tape. That embodiment allows forincreased lead density. An additional spacer 50 may be placed betweenleads 18 to prevent a short between the leads 18. The spacer 50 may bemade of the same materials as the deformable structure 20 discussedhereinabove with respect to FIGS. 1-4, so that the spacer 50 compensatesfor non-uniformities, such as on the substrate 12. The spacer 50 may bea dielectric so as to insulate signals on the leads 18.

[0039] The nature of the present invention and its preferred embodimentsas described herein allows the present invention to overcome many of thedifficulties of increasing the density of packages on a substrate. Thepresent invention can be used with or without a vertical packagingdesign, allowing for an increase in density through its method ofadjustment to non-uniformities. In addition, when adjusting tonon-uniformities on a substrate via the method explained herein, thereis a significant decrease in the risk that the lead from an integratedcircuit package will bend, break, or make poor contact with thesubstrate at the interconnect point. The present invention therebyensures improved electrical performance of IC packages.

[0040] The present invention as described herein may be used with orwithout L-shaped leads. When the present invention is used with L-shapedleads, the risk that the base of such leads will rub the bottom of thepackage, even when the exposed portion of the L is minimized, is greatlyreduced. The present invention also provides for the use of new, variedlead types, such as tape leads. These tape leads may be used in anover/under configuration, enhancing the number of interconnect pointsavailable within the area covered by the IC package on the substrate.The use of non-standard lead configurations connected via an LOC methodenables the exposure of one face of a die within the package, greatlyenhancing thermal properties.

[0041] The present invention has been described in connection with thepreferred embodiments thereof. Those of ordinary skill in the art willrecognize that many modifications and variations may be employed. Forexample, the embodiments illustrated in FIGS. 5-9 may be used eitherwith or without the deformable structures 20 described with respect toFIGS. 1-4. All such modifications and variations are intended to becovered by the foregoing description and the following claims.

1. A device, comprising: a circuit; a lead having a first end connectedto said circuit and having a second end; a deformable structureconnected to said second end of said lead.
 2. The device of claim 1,wherein said circuit is an integrated circuit.
 3. The device of claim 2,wherein said circuit is a memory device.
 4. The device of claim 2,wherein said circuit is selected from a group comprising a dynamicmemory device and a static memory device.
 5. The device of claim 1,wherein said device includes a plurality of leads.
 6. The device ofclaim 5, wherein the device includes a plurality of deformablestructures, and each of said plurality of deformable structures isconnected to one of said plurality of leads.
 7. The device of claim 5,wherein said deformable structure is connected to said plurality ofleads.
 8. The device of claim 1, wherein said deformable structure isformed from a material selected from a group comprising polymers andelastomers.
 9. The device of claim 1, wherein said deformable structureis resilient.
 10. The device of claim 1, wherein said deformablestructure is connected to a plurality of leads.
 11. The device of claim1, wherein said deformable structure is a conductor.
 12. The device ofclaim 1, wherein said deformable structure is a dielectric.
 13. Thedevice of claim 1, wherein said deformable structure is an adhesive. 14.The device of claim 1, further comprising an adhesive between said leadand said deformable structure.
 15. The device of claim 1, furthercomprising a conductor connected to both said lead and said deformablestructure.
 16. The device of claim 15, wherein said conductor is in aform of tape and includes an adhesive.
 17. A circuit board, comprising;a substrate; and a deformable structure connected to said substrate. 18.The circuit of claim 17, further comprising a device including a circuitand a lead, said lead having a first end connected to said circuit andhaving a second end connected to said deformable structure.
 19. Thecircuit board of claim 18, wherein said circuit board includes aplurality of devices.
 20. The circuit board of claim 19, wherein saiddeformable structure is connected to said plurality of devices.
 21. Thecircuit board of claim 17, wherein said circuit board includes aplurality of deformable structures.
 22. The circuit board of claim 17,further comprising an adhesive between said lead and said deformablestructure.
 23. The circuit board of claim 17, further comprising aconductor connected to said deformable structure.
 24. A device,comprising: a circuit having an active side and a non-active side; apackage enclosing the active side of said circuit and not enclosing aportion of the non-active side of said circuit; a lead having a firstend connected to the active side of said circuit via a lead-over-chipconnection, and having a second end extending from said package.
 25. Thedevice of claim 24, wherein said circuit has an edge and said package isconnected to the edge of said circuit.
 26. The device of claim 24,wherein said circuit has a plurality of edges and said package isconnected to at least one of the edges of said circuit.
 27. The deviceof claim 24, wherein said second end of said lead is L-shaped.
 28. Adevice, comprising: a circuit; a lead formed from a flexible conductor,said lead having a first end connected to said circuit.
 29. A device,comprising: a circuit; a package enclosing said circuit; a lead formedfrom a flexible conductor and an adhesive, said lead having a first endconnected to said circuit, having a portion connected to said package,and having a second end extending from said package.